1. Field of the Invention
This invention relates to a cooling unit for improving the radiation efficiency of a heat generating component, such as a semiconductor package and an electric apparatus, such as a portable computer provided with such a cooling unit.
2. Description of the Related Art
Notebook-type portable computers, PDAs (personal digital assistants) and other portable electronic apparatuses typically comprise a semiconductor package for processing multimedia information in the form of characters, sounds, and images. These days, such semiconductor packages consume more and more energy as their information processing rates are increased, and as they are made to provide more multi-functionally. As a result, they generate proportionally more heat than ever.
Under these circumstances, it is necessary to improve the radiation efficiency of the semiconductor package in order to ensure the stability of operation of the electric apparatus. In other words, it is indispensable that the semiconductor package be provided with any of a variety of available radiation/cooling means, such as a heat sink.
Conventional heat sinks have a heat receiving portion, which is thermally connected to the IC chip of the semiconductor package. If the IC chip and the heat receiving portion are separated from each other by a gap, the gap operates as a thermal insulation layer. Then, the transmission of heat from the IC chip to the heat receiving portion is blocked by the gap. Therefore, conventionally, the gap, if any, between the IC chip and the heat receiving portion is filled with thermally conductive grease, or a thermally conductive sheet is arranged in the gap. With such an arrangement, heat can be reliably transmitted from the IC chip to the heat receiving portion to improve the radiation efficiency of the IC chip.
In recent years, BGA (ball grid array) packages have constituted the mainstream of semiconductor packages of electronic apparatuses. A BGA package is provided on the surface mount device (SMD) located opposite to the IC chip with a number of solder balls arranged in the form of a grid. When BGA packages are mounted on respective circuit substrates, their heights can be dispersed within a range of xc2x10.25 mm.
On the other hand, a heat sink is fitted to the circuit substrate so as to cover the BGA package. Heat sinks are typically formed by way of injection molding of an aluminum alloy that is highly thermally conductive. However, the various parts including the heat receiving portion of a heat sink produced by injection molding can inevitably show dimensional variances due to solidification and contraction. Therefore, the distance from the heat receiving portion to the circuit substrate can vary considerably when the heat sink is fitted to the latter.
Thus, the gap between the heat receiving portion of the heat sink and the IC chip can become significantly large due to the dispersion of height of the BGA package and the dimensional inaccuracy of the heat sink. When the gap separating the IC chip and the heat sink becomes large, the thickness of the grease or the thermally conductive sheet interposed between them has to be raised correspondingly. Then, the zone thermally connecting the IC chip and the heat receiving portion shows a large thermal resistance.
Additionally, the contact area of the zone thermally connecting the IC chip and the heat receiving portion is substantially as large as the flat surface area of the IC chip. In other words, it is by far smaller than the surface area of the heat receiving portion. Thus, the heat transmission path connecting the IC chip and the heat receiving portion shows a small cross section, and hence heat has to be moved at a very high rate per unit area of the thermally connecting zone. Then, the IC chip and the heat receiving portion show a large temperature difference, and heat cannot be transmitted efficiently from the IC chip to the heat sink.
Therefore, it is an object of the present invention to provide a cooling unit that can effectively absorb the dimensional variances of the zone thermally connecting the heat generating component that may typically be an IC chip and the heat sink, and efficiently transmit heat from the heat generating component to the heat sink to improve the radiation efficiency of the heat generating component.
Another object of the present invention is to provide an electronic apparatus containing such a cooling unit.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out herein after.